Silane-crosslinkable ethylene-propylene copolymer and crosslinked body of the same

Abstract

A polyolefin-based thermoplastic elastomer and a crosslinked body of the same which can undergo a silane-crosslinking process excellent in productivity and have a rubber property required as a substitute material for EPDM is disclosed herein and can use a silane-crosslinkable ethylene-propylene copolymer characterized in that an organic peroxide (B) and a silane coupling agent (C) are compounded with an ethylene-propylene copolymer resin (A) which comprises 5 to 25% by mass of an ethylene component and 75 to 95% by mass of a propylene component, and whose MFR measured at 230° C. and with a load of 2.16 kg applied is 20.0 g/10 min or less. and further a compounded amount of the organic peroxide is 0.1 to 0.6 pts. mass based on 100 pts. mass of the ethylene-propylene copolymer resin (A) and a one-minute half-life temperature of the organic peroxide is 175.2° C. or less.

What is claimed is: 
     
       1. A crosslinked body for connecting electric cables, comprising:
 a cross-linked silane-crosslinkable ethylene-propylene graft copolymer containing an insulating inorganic filler, the cross-linked silane-crosslinkable ethylene-propylene graft copolymer being obtained by crosslinking a silane-crosslinkable ethylene-propylene graft copolymer having the insulating inorganic filler incorporated therein during a graft modification, 
 wherein the silane-crosslinkable ethylene-propylene graft copolymer having the insulating inorganic filler incorporated therein during the graft modification is obtained by compounding an organic peroxide (B), a silane coupling agent selected from vinyl trimethoxysilane and/or vinyl triethoxysilane (C), and the insulating inorganic filler (D) with an ethylene-propylene random copolymer resin (A), wherein the ethylene-propylene random copolymer resin has an isotactic structure, an ethylene component and a propylene component being 5 to 25% by mass and 75 to 95% by mass, respectively, and a melt mass flow rate measured at 230° C. and with a load of 2.16 kg applied is 20.0 g/10 min or less, wherein the organic peroxide (B) is present in an amount of 0.1 to 0.6 pts. mass based on 100 pts. mass of the ethylene-propylene copolymer resin (A) and a one-minute half-life temperature of the organic peroxide (B) is between 150° C. and 166° C., 
 wherein the crosslinked body has a heat deformation ratio of 35% or less which indicates a reduction rate X % determined by a formula X=(t 0 −t 1 )/t 0 *100, where t 0  denotes thickness of a test piece before heating and t 1  denotes thickness thereof after heating, the thickness t 1  being determined in such a manner that the test piece is made into a rectangular shape that is 2 mm thick, 15 mm wide, and 30 mm long, and after heating the test piece at 100° C. for 30 min., a load of 2.0 kg is applied to the test piece, followed by further heating the test piece at the same temperature for 30 min. and thereafter the thickness t 1  is measured, so that the thickness t 1  is obtained, and 
 an AC dielectric breakdown strength of the crosslinked body is 25 kV/mm or more which is determined by a formula AC dielectric breakdown strength (kV/mm)=AC dielectric breakdown voltage (kV)/thickness of test piece (mm), obtained by the following procedure: according to JIS C2110-1 electrodes are set at an approximately central portion of a test piece of 1 mm thick between upper and lower portions of the test piece, an AC voltage is boosted from 0V at a constant rate (1 kV/10 min.) and an AC breakdown voltage is measured. 
 
     
     
       2. A crosslinked body for connecting electric cables, comprising:
 a cross-linked silane-crosslinkable ethylene-propylene graft copolymer containing an insulating inorganic filler, the cross-linked silane-crosslinkable ethylene-propylene graft copolymer being obtained by crosslinking a silane-crosslinkable ethylene-propylene graft copolymer having the insulating inorganic filler incorporated therein during a graft modification, 
 wherein the silane-crosslinkable ethylene-propylene graft copolymer having the insulating inorganic filler incorporated therein during the graft modification is obtained by compounding an organic peroxide (B), a silane coupling agent selected from vinyl trimethoxysilane and/or vinyl triethoxysilane (C), and the insulating inorganic filler (D) with an ethylene-propylene random copolymer resin (A), wherein the ethylene-propylene random copolymer resin has an isotactic structure, an ethylene component and a propylene component being 5 to 25% by mass and 75 to 95% by mass, respectively, and a melt mass flow rate measured at 230° C. and with a load of 2.16 kg applied is 20.0 g/10 min or less, wherein the organic peroxide (B) is present in an amount of 0.1 to 0.6 pts. mass based on 100 pts. mass of the ethylene-propylene copolymer resin (A) and a one-minute half-life temperature of the organic peroxide (B) is between 150° C. and 166° C., 
 wherein the crosslinked body has a residual strain ratio of 60% or less which is determined by a formula (l 1 −l 0 )/l 0 *100, where l 1  denotes a length of a test piece after applying tension thereto and l 0  denotes a length thereof before applying tension thereto, the length l 1  being determined in such a manner that the test piece is made into a rectangular shape that is 2 mm thick, 10 mm wide, and 50 mm long except for a length of grippers, and after putting the test piece into a test machine heated at 90° C. to heat the test piece for 5 minutes therein, the test piece is extended at a tension rate of 50 mm/min. till its strain ratio reaches 250% and immediately after that, the test piece thus extended is turned back to normal at the rate of 50 mm/min. and at the moment a stress caused by the extending action becomes zero, a distance of the test piece between grippers is measured, so that the length l 1  is obtained from the distance, 
 an AC dielectric breakdown strength of the crosslinked body is 25 kV/mm or more which is determined by a formula AC dielectric breakdown strength (kV/mm)=AC dielectric breakdown voltage (kV)/thickness of test piece (mm), obtained by the following procedure: according to JIS C2110-1 electrodes are set at an approximately central portion of a test piece of 1 mm thick between upper and lower portions of the test piece, an AC voltage is boosted from 0V at a constant rate (1 kV/10 min.) and an AC breakdown voltage is measured. 
 
     
     
       3. The crosslinked body according to  claim 1 , wherein a compounded amount of the silane coupling agent (C) is 1 to 5 pts. mass based on 100 pts. mass of the ethylene-propylene copolymer resin (A). 
     
     
       4. The crosslinked body of  claim 1 , further comprising a softener. 
     
     
       5. The crosslinked body according to  claim 1 , wherein a compounded amount of the insulating inorganic filler is 10 to 150 pts. mass based on 100 pts. mass of the silane-crosslinkable ethylene-propylene graft copolymer. 
     
     
       6. The crosslinked body according to  claim 4 , wherein a compounded amount of the softener is 5 to 50 pts. mass based on 100 pts. mass of the insulating inorganic filler. 
     
     
       7. The crosslinked body according to  claim 2 , wherein a compounded amount of the silane coupling agent (C) is 1 to 5 pts. mass based on 100 pts. mass of the ethylene-propylene copolymer resin (A). 
     
     
       8. The crosslinked body of  claim 2 , further comprising a softener. 
     
     
       9. The crosslinked body according to  claim 8 , wherein a compounded amount of the softener is 5 to 50 pts. mass based on 100 pts. mass of the insulating inorganic filler. 
     
     
       10. The crosslinked body according to  claim 2 , wherein a compounded amount of the insulating inorganic filler is 10 to 150 pts. mass based on 100 pts. mass of the silane-crosslinkable ethylene-propylene graft copolymer. 
     
     
       11. The crosslinked body of  claim 1 , wherein a dielectric breakdown is generated beyond 360 minutes obtained by the following procedure: according to JIS C2136, a contaminating liquid (ammonia water) is started to be supplied (0.3 ml/min.) onto the surface of a test piece of 50 mm*120 mm*6 mm and with the contaminating liquid allowed to flow constantly thereonto, a voltage is boosted up to 3.5 kV to measure a time required to cause its dielectric breakdown. 
     
     
       12. The crosslinked body according to  claim 11 , wherein a compounded amount of the insulating inorganic filler is in the range of 50 to 100 pts. mass, based on 100 pts. mass of the ethylene-propylene copolymer resin (A). 
     
     
       13. The crosslinked body according to  claim 12 , wherein the AC dielectric breakdown strength is 27.6 kV/mm or more which is determined by a formula AC dielectric breakdown strength (kV/mm)=AC dielectric breakdown voltage (kV)/thickness of test piece (mm), obtained by the following procedure: according to JIS C2110-1 electrodes are set at an approximately central portion of a test piece of 1 mm thick between upper and lower portions of the test piece, an AC voltage is boosted from 0V at a constant rate (1 kV/10 min.) and an AC breakdown voltage is measured. 
     
     
       14. The crosslinked body of  claim 2 , wherein a dielectric breakdown is generated beyond 360 minutes obtained by the following procedure: according to JIS C2136, a contaminating liquid (ammonia water) is started to be supplied (0.3 ml/min.) onto the surface of a test piece of 50 mm*120 mm*6 mm and with the contaminating liquid allowed to flow constantly thereonto, a voltage is boosted up to 3.5 kV to measure a time required to cause its dielectric breakdown. 
     
     
       15. The crosslinked body according to  claim 14 , wherein a compounded amount of the insulating inorganic filler is in the range of 50 to 100 to pts. mass, based on 100 pts. mass of the ethylene-propylene copolymer resin (A). 
     
     
       16. The crosslinked body according to  claim 15 , wherein the AC dielectric breakdown strength is 27.6 kV/mm or more which is determined by a formula AC dielectric breakdown strength (kV/mm)=AC dielectric breakdown voltage (kV)/thickness of test piece (mm), obtained by the following procedure: according to JIS C2110-1 electrodes are set at an approximately central portion of a test piece of 1 mm thick between upper and lower portions of the test piece, an AC voltage is boosted from 0V at a constant rate (1 kV/10 min.) and an AC breakdown voltage is measured. 
     
     
       17. The crosslinked body according to  claim 1 , wherein a compounded amount of insulating inorganic filler is in a range of 100 to 150 pts mass based on 100 pts mass of the ethylene-propylene copolymer resin(A). 
     
     
       18. The crosslinked body according to  claim 2 , wherein a compounded amount of insulating inorganic filler is in a range of 100 to 150 pts mass based on 100 pts mass of the ethylene-propylene copolymer resin(A). 
     
     
       19. The crosslinked body according to  claim 17 , wherein the AC dielectric breakdown strength of the crosslinked body is 30.2 kV/mm or more which is determined by a formula AC dielectric breakdown strength (kV/mm)=AC dielectric breakdown voltage (kV)/thickness of test piece (mm), obtained by the following procedure: according to JIS C2110-1 electrodes are set at an approximately central portion of a test piece of 1 mm thick between upper and lower portions of the test piece, an AC voltage is boosted from 0V at a constant rate (1 kV/10 min.) and an AC breakdown voltage is measured. 
     
     
       20. The crosslinked body according to  claim 18 , wherein the AC dielectric breakdown strength of the crosslinked body is 30.2 kV/mm or more which is determined by a formula AC dielectric breakdown strength (kV/mm)=AC dielectric breakdown voltage (kV)/thickness of test piece (mm), obtained by the following procedure: according to JIS C2110-1 electrodes are set at an approximately central portion of a test piece of 1 mm thick between upper and lower portions of the test piece, an AC voltage is boosted from 0V at a constant rate (1 kV/10 min.) and an AC breakdown voltage is measured.